1. Field of the Invention
The present invention relates to an optical device comprising optical elements, more particularly, to a structure for mounting optical elements on a base plate.
2. Description of the Prior Art
Optical communication systems make use of numerous optical devices, such as a device for coupling light, a device for multiplexing light components of different wavelengths, a light source, and a device for attenuating light. Such optical devices include an optical element for emitting light and an optical element for receiving light, each optical element being mounted on a base plate and secured thereto. The usual optical element consists of a cylindrical sleeve housing a lens and one end of an optical transmission fiber.
Light from an optical transmission fiber of a first optical element for emitting light is transmitted to the optical transmission fiber of a second optical element for receiving light via a functional optical element, such as a filter, lens, prism, mirror, or switching element, disposed therebetween. Misalignment or inclination of the optical axis of the second optical element for receiving light (this axis coincides with the axis of the optical transmission fiber installed therein) with respect to the optical axis of the first optical element for emitting light results in increased transmission loss in the optical device. This is especially true when a single-mode type optical fiber is used, since the diameter of the core of the single-mode fiber is very small (about 10 .mu.m) compared with the core of a multi-mode fiber (about 50 .mu.m).
To minimize transmission loss in an optical device, the optical axis of the second optical element for receiving light must be precisely aligned with the optical axis of the first optical element for emitting light. The optical axis of the first optical element for emitting light is invariably slightly inclined with respect to the base plate surface since accuracy in producing the element and attaching it to the base plate is limited. Therefore, the optical axis of the second optical element for receiving light must be capable of slightly inclining with respect to the base plate surface to properly align it with the axis of the optical element for emitting light.
In a conventional optical device, an optical element for receiving light is mounted on and secured to the base plate as follows. First, the cylindrical sleeve of the optical element is disposed above the base plate at the position where the optical axis of the optical element for receiving light is aligned with the optical axis of the optical element for emitting light and held there temporarily by an appropriate temporary holder. Then, a support member is disposed between the cylindrical sleeve and the base plate. After that, the cylindrical sleeve is secured to the support member surface by means of a synthetic resin adhesive agent. The support member is also secured to the base plate by means of the adhesive agent. The temporary holder which held the cylindrical sleeve at that position is then removed.
In the conventional structure, the cylindrical sleeve contacts the support member surface only along a generating line of the cylindrical body. Therefore, the sleeve is easily displaced by the application of force thereto. Therefore, it is difficult to keep the sleeve reliably secured to the support member at the desired position. The problem is compounded in that the adhesive agent degrades when the ambient temperature or humidity changes. Also, the process for securing the sleeve to the support member requires a considerable amount of time due to the need to allow the adhesive agent to dry.